This invention relates to pens which utilize a fluid ink an whose writing tips are axially positionable with respect to an outer sheath.
Various types of pens using an aqueous or non-aqueous fluid are in widespread use for writing, drawing, painting or marking purposes, and may collectively be referred to as marking pens. Said fluids, which may be inks having soluble dyes, or paints having dispersed pigments, may be generically referred to as marking fluids. Many of such pens are provided with protective caps which prevent evaporation of the fluid and prevent accidental contact of the fluid with the clothing or skin of the user or with other objects. However, the placement and removal of the cap is troublesome, and the cap is frequently misplaced.
Marking pens which avoid the need for a protective cap are well known and generally employ a mechanism whereby the tip of the pen can be retracted into a protective enclosure within an elongated sheath comprising the outer body of the pen. Marking pens of such construction are disclosed for example in U.S. Pat. Nos. 4,218,154; 3,652,172; and 4,540,300. The protective enclosures and associated retracting mechanisms are, however, generally of complex, expensive construction and do not endure long term use.
A significantly improved retractable tip marking pen is disclosed in U.S. Pat. No. 4,711,592 wherein the tip, in its retracted position, is enclosed within a chamber that prevents drying of the marking fluid. The chamber is fashioned within an elastomeric sealing member positioned within the outer sheath of the pen adjacent the lower extremity thereof. When the writing mechanism within the sheath is pushed downwardly to its writing position, it carries the sealing member, causing it to open and permit axial emergence of the tip.
The means disclosed in U.S. Pat. No. 4,711,592 whereby the writing mechanism carries the sealing member downwardly is an annular activating shoulder which fits into a retaining groove within the sealing member. Careful study of such construction has shown that repeated interaction between the activating shoulder and the sealing member results in stretching, wearing and deformation of the elastomeric material comprising the sealing member. Such factors degrade the seal that is formed when the activating shoulder is seated within the retaining groove. Such factors also cause the activating shoulder to exit the retaining groove before the sealing member reaches its lowermost, open position. Such premature disengagement causes ink to be undesirably deposited upon the lowermost portion of the sealing member. The lowermost portion of the sealing member then contaminates the activating shoulder with ink, which in turn contaminates the retaining groove.
The device of U.S. Pat. No. 4,711,592 further requires that the sealing member, in its downwardmost, open position be secured by frictional holding means associated with the sheath. However, such holding means have been found to malfunction when the sealing member is not carried downwardly with sufficient force by the writing mechanism, when the holding means is contaminated with ink or lubricant or when the pen is jarred. In such situations, upon upward retraction of the writing mechanism, the activating shoulder engages the lowermost portion of the sealing member, causing it to close tightly upon the writing mechanism to prevent its complete upward movement.
It is accordingly an object of the present invention to improve the pen of U.S. Pat. No. 4,711,592.
In particular, it is a further object of this invention to cause the sealing member to be downwardly urged independently of the writing member.
It is another object of the present invention to provide a pen of the aforesaid nature wherein said sealing member is held in its open position by means other than frictional restraint.
These objects and other objects and advantages of the invention will be apparent from the following description.